Photonic crystals: properties and potential applications

Photonic crystals is an area rich in intriguing phenomena that rise the prospects for realizing unusual photonic devices. For instance, in the vicinity of the photonic band gap the propagation direction becomes super sensitive to the wavelength and to the angle at which the beam impinges the crystal. These superprism phenomena can be used for high resolution demultiplexing or beam steering. In addition, a very unique effect of negative refraction implying self-focusing of the beam suggests possibilities for three dimensional, real image photography. By forming defects in the crystal lattice one can "trap" light at wavelengths within the photonic band gap and force it to oscillate or be guided along the defects. The concept of a defect waveguide in the one-dimensional version of a photonic crystal, i.e. a multilayer Bragg reflector, is known under the name Bragg reflection waveguides since the early 70s. In 1987 it was shown that photonic band gaps and light trapping in defect waveguides are possible in all three dimensions. Photonic waveguides in twoand three dimensions allow very sharp bends without radiation loss, thus enabling ultra compact integrated circuits. In active materials emission rate and its angular spectrum can be controlled by the photonic band gap design, which can be utilized for very efficient, narrow-band and highly directional light emitting diodes, or "zero-threshold" lasers. Photonic crystals open possibilities for the next-generation multifunctional integrated components that provide increased functionality in about 100 times smaller footprint than offered by today\´s integrated optics.